# What is Negative Temperature and How Does it Work?

• hagopbul
In summary, reaching 0 Kelvin is not possible according to the 3rd law of thermodynamics. Quantum mechanics also supports this idea, as knowing the momentum of all particles would mean uncertainty in their position. Objects with lower temperatures absorb more heat in a given amount of time, and a zero temperature object would absorb infinite heat in a short time. Negative temperature systems exist, where they become "cooler" when heated up.
hagopbul
so is it impossible to Reich the 0 Kelvin or not

3rd law of thermodynamics says yes. You can only get asymptotically close.

You would need something below zero to cool your system up to 0K. But 0K is the lowest temperature possible. So there are no means you can use to get to 0K.

According to QM the answer is no, because if the momentum of all the particles is known to be 0 then you have no knowlage of the position of the particles - but if you know where they are then there's always some uncertainty in their momentum.

Fix an object at temperature x. Now, if I have several other objects of lower temperatures $$y_1,y_2,...,y_n$$. What do these y values represent?

The answer is that the objects with the smaller y values will absorb more heat in a given amount of time. The problem of course with a zero temperature object is that it would absorb infinite heat in an arbitrarily short time i.e. for any objects x, y and any amount of wattage there are temperatures the objects could have could have so as to exchange energy at that rate.

Negative temperature is not a contradiction, these are systems that become "cooler" when you heat them up, that is they become more willing to receive energy at from another object of given temperature.

## 1. Can 0 Kelvin be reached in real life?

No, 0 Kelvin cannot be reached in real life. It is a theoretical temperature that represents absolute zero, the lowest possible temperature where all molecular motion stops.

## 2. What is the coldest temperature ever achieved in a lab?

The coldest temperature ever achieved in a lab is 100 picokelvins (pK), which is only 0.0000000001 Kelvin above absolute zero.

## 3. Is it possible for an object to reach 0 Kelvin?

No, it is not possible for an object to reach 0 Kelvin. As an object cools down, it will eventually reach absolute zero, but it can never reach exactly 0 Kelvin due to the laws of thermodynamics.

## 4. What happens to matter at 0 Kelvin?

At 0 Kelvin, matter would have no thermal energy and would not be able to move or interact in any way. It would be in a state of absolute rest.

## 5. Why is 0 Kelvin considered the lowest possible temperature?

0 Kelvin is considered the lowest possible temperature because it represents the point at which all molecular motion stops. At this temperature, there is no thermal energy left to extract from a system, making it impossible to go any lower.

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